When using programs like Adobe Photoshop or other similar graphic heavy programs, your Mac is using its graphics card in an overtime fashion. This is particularly the case when your Mac has only 4 GB of RAM. Such graphics heavy programs typically require 8 GB of RAM to run smoothly and sometimes even 16 GB is recommended as the ideal amount of RAM to be present.
When your graphics card constantly overclocks itself to keep up with the graphic program’s heavy demands, it can go berserk and misconfigure itself, causing it to improperly communicate with the Mac’s CPU. When this communication shutdown happens, your Mac can start to slow down heavily. If you ever wondered why is my mac so slow all of a sudden, this is probably one of the reasons why.
To overcome this issue, you want to first try resetting your Mac’s SMC or system controller reset. This is a soft reset that basically reconfigures your Mac’s hardware settings. This will not affect your user data. You might have to reset your time and a few basic system preferences but. To do a SMC reset, you will need to shut down your Mac and unplug it from the wall before re-plugging it back in and then restarting it by pressing a combination of keys. Please look up Apple’s website about how to carry out a SMC reset. You can also attempt a PRAM reset that will do the same thing as a SMC reset, but just focusing on memory modules. Again, a PRAM reset will also not affect your user data.
Try restarting your Mac after these two resets to see if your Mac’s video card has fixed itself. If problems still persist, it could mean that your video card has become outdated or even glitch prone, meaning that you have no choice but to replace it with a newer video card.